U.S. patent application number 12/524737 was filed with the patent office on 2010-05-13 for silicon crystalline material and method for manufacturing the same.
This patent application is currently assigned to SUMCO TECHXIV CORPORATION. Invention is credited to Shinji Togawa, Ryosuke Ueda.
Application Number | 20100116194 12/524737 |
Document ID | / |
Family ID | 39673888 |
Filed Date | 2010-05-13 |
United States Patent
Application |
20100116194 |
Kind Code |
A1 |
Togawa; Shinji ; et
al. |
May 13, 2010 |
SILICON CRYSTALLINE MATERIAL AND METHOD FOR MANUFACTURING THE
SAME
Abstract
Provided is a silicon crystalline material, which is
manufactured by a CZ method to be used as a material bar for
manufacturing a silicon single crystal by an FZ method and has a
grasping section for being loaded in a crystal growing furnace
employing the FZ method without requiring mechanical processing. A
method for manufacturing such silicon crystalline material is also
provided. The silicon crystalline material is manufactured by the
silicon crystal manufacturing method employing the CZ method and is
provided with the grasping section, which is manufactured in a
similar way as a shoulder portion, a straight body portion and a
tail portion in a silicon crystal growing step employing the CZ
method, and is loaded in a single crystal manufacturing apparatus
employing the FZ method to grow single crystals. A seed-crystal
used in the silicon crystal manufacture employing the CZ method is
used as the grasping section. The grasping section is manufactured
by temporarily changing crystal growing conditions to form a
protruding section or a recessed section on the outer circumference
surface of the straight body section or by forming a dent on the
shoulder portion of the straight body portion, at the time of
manufacturing the silicon crystal by the CZ method.
Inventors: |
Togawa; Shinji; (Nagasaki,
JP) ; Ueda; Ryosuke; (Nagasaki, JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
SUMCO TECHXIV CORPORATION
Nagasaki
JP
|
Family ID: |
39673888 |
Appl. No.: |
12/524737 |
Filed: |
January 23, 2008 |
PCT Filed: |
January 23, 2008 |
PCT NO: |
PCT/JP2008/050882 |
371 Date: |
July 28, 2009 |
Current U.S.
Class: |
117/13 ; 117/30;
423/348 |
Current CPC
Class: |
C30B 15/22 20130101;
C30B 13/285 20130101; C30B 13/32 20130101; C30B 29/06 20130101 |
Class at
Publication: |
117/13 ; 423/348;
117/30 |
International
Class: |
C30B 15/28 20060101
C30B015/28; C01B 33/021 20060101 C01B033/021; C30B 15/22 20060101
C30B015/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2007 |
JP |
2007-021044 |
Claims
1. A silicon crystal material that is manufactured by a CZ method
and used for manufacturing a silicon single crystal by an FZ
method, the silicon crystal material comprising: a shoulder portion
that gradually grows in diameter; a straight body portion that is
cylindrical; a tail portion that gradually reduces in diameter; and
a gripped portion that is gripped by a gripper during manufacturing
of the silicon single crystal by the FZ method and that enables
loading of the silicon crystal material into a furnace and growth
of a single crystal, wherein the gripped portion is, as with the
shoulder portion, the straight body portion, and the tail portion,
formed in a manufacturing process of the silicon crystal material
by the CZ method.
2. The silicon crystal material according to claim 1, wherein the
gripped portion is a convex portion formed along a circumference of
the straight body portion.
3. The silicon crystal material according to claim 1, wherein the
gripped portion is a concave portion formed along a circumference
of the straight body portion.
4. The silicon crystal material according to claim 1, wherein the
gripped portion is a constricted portion formed above the shoulder
portion.
5. A silicon crystal material that is manufactured by a CZ method
and used for manufacturing a silicon single crystal by an FZ
method, the silicon crystal material comprising: a shoulder portion
that gradually grows in diameter; a straight body portion that is
cylindrical; a tail portion that gradually reduces in diameter; and
a gripped portion that is gripped by a gripper during manufacturing
of the silicon single crystal by the FZ method and that enables
loading of the silicon crystal material into a furnace and growth
of a single crystal, wherein the gripped portion is a seed crystal
used in a manufacturing process of the silicon crystal material by
the CZ method.
6. A manufacturing method of a silicon crystal material used for
manufacturing a silicon single crystal by an FZ method, the silicon
crystal material comprising: a shoulder portion that gradually
grows in diameter; a straight body portion that is cylindrical; a
tail portion that gradually reduces in diameter; and a gripped
portion that is gripped by a gripper during manufacturing of the
silicon single crystal by the FZ method and that enables loading of
the silicon crystal material into a furnace and growth of a single
crystal, wherein the shoulder portion, the straight body portion,
the tail portion, and the gripped portion are formed by a CZ
method.
7. The manufacturing method of the silicon crystal material
according to claim 6, wherein the gripped portion is formed by
changing a crystal growth condition at a predetermined point of
time in a manufacturing process of the silicon crystal material by
the CZ method.
8. The manufacturing method of the silicon crystal material
according to claim 7, wherein the crystal growth condition is
changed by changing at least any one of single crystal growth rate
and temperature of raw material silicon melt.
9. A manufacturing method of an FZ silicon single crystal, in which
the silicon single crystal is manufactured by the FZ method using
the silicon crystal material according to claim 1.
10. A manufacturing method of an FZ silicon single crystal, in
which the silicon single crystal is manufactured by the FZ method
using the silicon crystal material according to claim 5.
Description
TECHNICAL FIELD
[0001] The present invention relates to a silicon crystal material
used as a raw material ingot for manufacturing a silicon single
crystal by the FZ method (floating zone melting method) and a
manufacturing method thereof, and particularly relates to a silicon
crystal material and a manufacturing method thereof for
manufacturing a large diameter of FZ silicon single crystal at low
cost.
BACKGROUND ART
[0002] Currently, silicon is typically used as a semiconductor that
is widely industrially used as a device for an integrated circuit
(IC) and a large-scale integrated circuit (LSI). A silicon single
crystal used in the semiconductor industry and the like is
manufactured from polycrystalline silicon as raw materials by the
floating zone melting method (FZ method for short) in which the
bar-shaped polycrystalline silicon is melted by induction heating
and a single crystal is grown, or by the Czochralski method (CZ
method for short) in which the polycrystal is heated and melted in
a crucible, a seed crystal is immersed in a melt and withdrawn
therefrom, and a single crystal ingot is grown below the seed
crystal.
[0003] A manufacturing method is selected from these methods in
accordance with usage of the single crystal. In general, a single
crystal manufactured by the FZ method is used for high resistivity
and a single crystal manufactured by the CZ method is used for low
to moderate resistivity.
[0004] In recent years, reduction in parasitic capacitance is
required in a semiconductor device for mobile communication and in
a leading-edge C-MOS device. It is reported that signal loss in
transmission and parasitic capacitance in Schottky barrier diode
can be effectively reduced by using a substrate of high
resistivity. Given this, a high resistivity silicon wafer
manufactured by the floating zone melting method (FZ method) is
used for manufacturing a power device such as a high-voltage power
device, a thyristor or the like.
[0005] Meanwhile, in recent years, a large diameter silicon wafer
is sought for improving performance and reducing cost of a
semiconductor device. Consequently, a large diameter FZ silicon
single crystal of at least 150 mm in diameter is required, and thus
development of a manufacturing method thereof has been awaited.
[0006] In a case of manufacturing a large diameter silicon single
crystal, particularly of at least 150 mm in diameter, by the FZ
method, a polycrystalline silicon material having a diameter of at
least 140 mm is considered to be preferably used as a raw material
ingot. For example, for manufacturing a silicon single crystal of
200 mm in diameter, a method using polycrystalline silicon having a
diameter of at least 145 mm as a silicon raw material ingot is
disclosed in Japanese Unexamined Patent Application Publication No.
2003-55089 (hereinafter referred to as Patent Document 1).
[0007] As described above, it is generally profitable to
manufacture a silicon single crystal from a silicon raw material
ingot with a diameter as large as possible, from a perspective of
productivity and the like. However, since a silicon raw material
ingot for polycrystalline silicon that is commercially available is
manufactured by vapor phase growth, it is difficult to manufacture
a large diameter polycrystalline silicon, particularly of at least
150 mm in diameter. In addition, polycrystalline silicon of a large
diameter has a drawback of having a nonuniform grain boundary
structure. Consequently, a problem of an extremely low yield is
reported, in a case of manufacturing a silicon single crystal of
200 mm in diameter by the FZ method using a polycrystalline silicon
raw material ingot of 160 mm in diameter, since a single
manufacturing process by the FZ method cannot make a single crystal
dislocation free and therefore the process must be repeated.
Furthermore, polycrystalline silicon of a large diameter has
another drawback of having a high unit cost.
[0008] On the other hand, an attempt is being made to manufacture
an FZ silicon single crystal by using a large diameter CZ silicon
crystal bar obtained by the CZ method (for example, see Japanese
Unexamined Patent Application Publication No. 2005-281076 and
2005-306653, hereinafter referred to as Patent Documents 2 and
3).
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0009] In a case of crystal growth by the FZ method, a silicon
crystal material, which is a raw material silicon bar, is required
to be maintained suspended in an FZ furnace. However, a common
silicon crystal material manufactured by the CZ method, which is
cylindrical, does not have a portion to be gripped. Consequently,
the silicon crystal material manufactured by the CZ method must be
subjected to cutting of a shoulder portion and a tail portion
thereof and mechanical processing for forming a groove and the
like, and then loaded into an FZ furnace, being gripped at the
groove or the like. In addition, fixing by a screw or the like is
required, as disclosed in Patent Documents 2 and 3. As described
above, since an operation for forming a groove or the like, which
is to be gripped, on the silicon crystal material is required, the
manufacturing process becomes complex, material is lost in the
operation, and cycle time becomes longer.
[0010] The present invention is made in view of the abovementioned
problems, and aims at providing a silicon crystal material that is
manufactured by the CZ method and used for manufacturing a silicon
single crystal by the FZ method, which can be loaded into and
withdrawn from an FZ furnace without requiring mechanical
processing, and a manufacturing method thereof.
Means for Solving the Problems
[0011] The present inventors have thoroughly researched in order to
solve the abovementioned problems. As a result, the present
inventors have found that a gripped portion, which is to be gripped
by a gripper and allows loading into and withdrawal from an FZ
furnace, can be formed by temporarily changing a growth condition
of crystal in manufacturing of a silicon raw material ingot by the
CZ method, which is used for manufacturing a silicon single crystal
by the FZ method, thus leading to the completion of the present
invention. More specifically, the present invention provides the
following.
[0012] In a first aspect of the present invention, a silicon
crystal material that is manufactured by a CZ method and used for
manufacturing a silicon single crystal by an FZ method includes: a
shoulder portion that gradually grows in diameter; a straight body
portion that is cylindrical; a tail portion that gradually reduces
in diameter; and a gripped portion that is gripped by a gripper
during manufacturing of the silicon single crystal by the FZ method
and that enables loading of the silicon crystal material into a
furnace and growth of a single crystal, in which the gripped
portion is, as with the shoulder portion, the straight body
portion, and the tail portion, formed in a manufacturing process of
the silicon crystal material by the CZ method.
[0013] According to the first aspect, the silicon crystal material
used for manufacturing a silicon single crystal by the FZ method
has a gripped portion, which allows loading the silicon crystal
material into an FZ single crystal manufacturing device and single
crystal growth therein, formed in a manufacturing process of the
silicon crystal material by the CZ method as with the shoulder
portion, the straight body portion, and the tail portion of the
silicon crystal. Therefore, the silicon crystal material
manufactured by the CZ method can be used as a raw material ingot
for manufacturing an FZ silicon single crystal without
post-processing for forming the gripped portion. This can reduce
loss of material due to the post-processing and cycle time for the
FZ silicon single crystal manufacturing.
[0014] According to a second aspect of the present invention, in
the silicon crystal material as described in the first aspect, the
gripped portion is a convex portion formed along a circumference of
the straight body portion.
[0015] According to the second aspect of the present invention,
since a convex portion is formed along a circumference of the
straight body portion, the silicon crystal material can be
maintained suspended by the convex portion being hooked by a
gripper, and easily loaded into an FZ single crystal manufacturing
device.
[0016] According to a third aspect of the present invention, in the
silicon crystal material as described in the first aspect, the
gripped portion is a concave portion formed along a circumference
of the straight body portion.
[0017] According to the third aspect of the present invention,
since a concave portion is formed along a circumferential direction
of the straight body portion, the silicon crystal material can be
maintained suspended by the concave portion being hooked by a
gripper, and easily loaded into an FZ single crystal manufacturing
device.
[0018] According to a fourth aspect of the present invention, in
the silicon crystal material as described in the first aspect, the
gripped portion is a constricted portion formed above the shoulder
portion.
[0019] According to the fourth aspect of the present invention,
since a constricted portion is formed above the shoulder portion,
the silicon crystal material can be maintained suspended by the
constricted portion being hooked by a gripper, and easily loaded
into an FZ single crystal manufacturing device.
[0020] In a fifth aspect of the present invention, a silicon
crystal material that is manufactured by a CZ method and used for
manufacturing a silicon single crystal by an FZ method includes: a
shoulder portion that gradually grows in diameter; a straight body
portion that is cylindrical; a tail portion that gradually reduces
in diameter; and a gripped portion that is gripped by a gripper
during manufacturing of the silicon single crystal by the FZ method
and that enables loading of the silicon crystal material into a
furnace and growth of a single crystal, in which the gripped
portion is a seed crystal used in a manufacturing process of the
silicon crystal material by the CZ method.
[0021] According to the fifth aspect of the present invention, the
silicon crystal material can be maintained suspended by the seed
crystal which is used in the manufacturing process thereof by the
CZ method being hooked by a gripper, and easily loaded into an FZ
single crystal manufacturing device. In addition, since the silicon
crystal material manufactured by the CZ method is used as a raw
material ingot, the seed crystal and a main crystal body (the
straight body portion) have a concentric rotational center.
Therefore there is no need for a centering operation for rotation
after loading into the FZ furnace and the processing can be further
simplified.
[0022] In a sixth aspect of the present invention, in a
manufacturing method of a silicon crystal material used for
manufacturing a silicon single crystal by an FZ method, the silicon
crystal material includes: a shoulder portion that gradually grows
in diameter; a straight body portion that is cylindrical; a tail
portion that gradually reduces in diameter; and a gripped portion
that is gripped by a gripper during manufacturing of the silicon
single crystal by the FZ method and that enables loading of the
silicon crystal material into a furnace and growth of a single
crystal, and the shoulder portion, the straight body portion, the
tail portion, and the gripped portion are formed by a CZ
method.
[0023] According to the sixth aspect of the present invention, the
gripped portion for maintaining the silicon crystal material
suspended inside an FZ furnace is formed by the CZ method, as with
the shoulder portion, the straight body portion, and the tail
portion. In other words, in manufacturing of a silicon crystal
material by the CZ method, the convex portion, the concave portion,
or the constricted portion is formed in a phase of growing the
straight body portion or in a phase where growth moves from a neck
portion to the shoulder portion or the like. Therefore, the silicon
crystal material manufactured by the CZ method can be used as a raw
material ingot for manufacturing an FZ silicon single crystal
without post-processing for forming the gripped portion. This can
reduce loss of material due to the post-processing and cycle time
for the FZ silicon single crystal manufacturing.
[0024] According to a seventh aspect of the present invention, in
the manufacturing method of a silicon crystal material as described
in the sixth aspect, the gripped portion is formed by changing a
crystal growth condition at a predetermined point of time in a
manufacturing process of the silicon crystal material by the CZ
method.
[0025] According to the seventh aspect of the present invention, in
the manufacturing process of the silicon crystal material by the CZ
method, diameter of crystal can be changed by changing a crystal
growth condition. Consequently, a concave portion and a convex
portion can be formed by, for example, changing a crystal growth
condition at a predetermined timing for a predetermined period of
time, in a phase of crystal growth in the straight body portion. In
addition, a constricted portion of a rhombus bead shape can be
formed by changing the crystal growth condition in a phase where
growth moves the shoulder portion or the like.
[0026] The crystal growth condition is changed by, for example,
increase and decrease in a single crystal growth rate and/or
raising and lowering of temperature of a melt obtained by melting a
raw material silicon polycrystal, in other words raising and
lowering of heating temperature.
[0027] According to an eighth aspect of the present invention, in
the manufacturing method of a silicon crystal material as described
in the seventh aspect, the crystal growth condition is changed by
changing at least any one of single crystal growth rate and
temperature of raw material silicon melt.
[0028] According to the eighth aspect of the present invention,
crystal diameter becomes larger by lowering single crystal growth
rate. On the other hand, crystal diameter becomes smaller by
raising the single crystal growth rate. Thus, a convex portion and
a concave portion can be formed on the straight body portion by
temporarily changing the single crystal growth rate in a phase of
crystal growth in the straight body portion. In addition, the
constricted portion having a substantially diamond-shape in the
vertical cross section (having a rhombus bead shape) can be formed
by temporarily changing the single crystal growth rate during
formation of the neck portion.
[0029] Furthermore, a convex portion and a concave portion can be
formed by temporarily changing temperature of a melt during
formation of the straight body portion, by raising and lowering
temperature of the melt, in other words heating temperature by a
heater. Moreover, the constricted portion having a substantially
diamond-shape in the vertical cross section (having a rhombus bead
shape) can be formed by temporarily changing temperature of the
melt during formation of a neck portion. This is because the melt
easily solidifies at low temperature and not at high temperature,
thereby changing crystallization. It should be noted that the
temperature of the melt is raised and lowered generally by raising
and lowering heating temperature by a heater.
[0030] In a ninth aspect of the present invention, in a
manufacturing method of an FZ silicon single crystal, the silicon
single crystal is manufactured by the FZ method using the silicon
crystal material according to any one the first to the fifth
aspects.
[0031] According to the ninth aspect of the present invention,
since the silicon crystal material as described in any one of the
first to the fifth aspects has the gripped portion formed in the
manufacturing process by the CZ method, the silicon crystal
material can be used, without post-processing for forming the
gripped portion thereon, for manufacturing a silicon single crystal
by the FZ method. This can reduce loss of material and cycle time
for manufacturing. In addition, since a large diameter silicon
crystal material can be obtained by the CZ method, a large diameter
silicon single crystal can be obtained by using the silicon crystal
material as a raw material ingot.
Effects of the Invention
[0032] The silicon crystal material according to the present
invention is manufactured in a silicon crystal manufacturing method
according to the CZ method and has the gripped portion that can be
mechanically gripped, formed in a crystal manufacturing process.
Therefore the silicon crystal material can be used, without
post-processing for forming the gripped portion thereon, as a raw
material ingot for the FZ method. This can reduce loss of material
in processing and cycle time for the FZ silicon single crystal
manufacturing. In addition, since the silicon crystal material
according to the present invention is manufactured by growing a
crystal by the CZ method, a large diameter crystal material can be
obtained at low cost. Consequently, a large diameter silicon single
crystal can be obtained at low cost by manufacturing an FZ single
crystal using this silicon crystal material as a raw material
ingot.
[0033] Furthermore, in the manufacturing method according to the
present invention, the gripped portion that can be mechanically
gripped can be formed only by temporarily changing a single crystal
growth rate and temperature of a melt, in other words heating
temperature by a heater, in a silicon crystal growth process by the
CZ method. Therefore, the silicon crystal material thus obtained
can be used as a raw material ingot for manufacturing an FZ silicon
single crystal without post-processing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a schematic vertical sectional view of a silicon
crystal material according to a first embodiment of the present
invention;
[0035] FIG. 2 is a schematic vertical sectional view of a silicon
crystal material according to a second embodiment of the present
invention;
[0036] FIG. 3 is a schematic vertical sectional view of a silicon
crystal material according to a third embodiment of the present
invention;
[0037] FIG. 4 is a schematic vertical sectional view of a silicon
crystal material according to a fourth embodiment of the present
invention;
[0038] FIG. 5 is a schematic partial sectional view illustrating an
example of an FZ single crystal manufacturing device according to
the present invention;
[0039] FIG. 6 is a partial sectional view schematically
illustrating a state where the silicon crystal material according
to the first embodiment of the present invention is gripped;
[0040] FIG. 7 is a partial sectional view schematically
illustrating a state where the silicon crystal material according
to the second embodiment of the present invention is gripped;
[0041] FIG. 8 is a partial sectional view schematically
illustrating a state where the silicon crystal material according
to the third embodiment of the present invention is gripped;
and
[0042] FIG. 9 is a partial sectional view schematically
illustrating a state where the silicon crystal material according
to the fourth embodiment of the present invention is gripped.
PREFERRED MODE FOR CARRYING OUT THE INVENTION
[0043] A silicon crystal material and a manufacturing method
thereof according to the present invention are described in detail
hereinafter.
[0044] The silicon crystal material according to the present
invention is characterized by that the silicon crystal material is
manufactured in a silicon crystal manufacturing method according to
the CZ method; and has a gripped portion that is attached to an FZ
single crystal manufacturing device and allows the silicon crystal
material to be maintained suspended, where the gripped portion is
formed in manufacturing of a silicon crystal by the CZ method not
by post-processing, or is a seed crystal used for manufacturing a
silicon crystal by the CZ method. In addition, the manufacturing
method of a silicon crystal material according to the present
invention is characterized by forming the gripped portion on the
silicon crystal by temporarily changing a crystal growth condition
in a manufacturing process of the silicon crystal by the CZ
method.
[0045] Embodiments of the silicon crystal material according to the
present invention are described hereinafter with reference to the
drawings. It should be noted that an embodiment of the present
invention and a technical scope of the present invention are not
limited to the following embodiments. In the following description
of the embodiments, similar components are designated by the same
reference numerals, with the description thereof simplified or
omitted.
Silicon Crystal Material With Convex Gripped Portion
[0046] FIG. 1 is a sectional view schematically illustrating a
silicon crystal material according to a first embodiment of the
present invention. A silicon crystal material 1 is composed of: a
straight body portion 2; a convex portion (gripped portion) 3 that
is formed in an annular shape on a periphery of the straight body
portion 2; a neck portion 4 formed during single crystal growth of
a CZ crystal; a shoulder portion 5 that is continuous with the neck
portion 4 and constitutes an upper portion of the straight body
portion 2; and a tail portion 6 that constitutes a lower portion of
the straight body portion 2. The convex portion (gripped portion) 3
is formed in a manufacturing process of a silicon crystal by the CZ
method, on a periphery of the straight body portion 2, so as to
have a diameter larger than an external diameter of the straight
body portion 2. It should be noted that, although the convex
portion (gripped portion) 3 is formed on the tail portion 6 side in
the present embodiment, the present invention is not limited
thereto and the convex portion 3 can also be formed on the shoulder
portion 5 side.
[0047] Although the diameter of the convex portion (gripped
portion) 3 varies dependent on a shape, a structure and the like of
a gripper for gripping the silicon crystal material, the diameter
of the convex portion (gripped portion) 3 is preferably greater
than the external diameter of the straight body portion 2 by about
6 to 20 mm. In addition, a length thereof is preferably about 7 to
25 mm. As used herein, the length means a size corresponding to a
thickness in a vertical direction (a longitudinal direction of the
straight body portion).
Manufacturing Method
[0048] The silicon crystal material 1 with the convex portion 3 as
the gripped portion can be manufactured in a conventional
manufacturing method of a silicon crystal by the CZ method. That
is, a silicon crystal material is manufactured by: filling a
crucible such as a quartz crucible with a raw material which is an
agglomerate of silicon polycrystal; immersing a seed crystal into a
raw material melt, in which the silicon polycrystal is melt down by
heating by a heater and the like; and growing a crystal up to a
predetermined size, for example 155 mm in diameter and 1150 mm in
length of the straight body portion while rotating the seed crystal
and the crucible in inverse directions. It should be noted that a
crystal growth condition is set in accordance with a desired
diameter of crystal.
[0049] In a crystal growth process, the crystal growth condition is
temporarily changed by, for example, temporarily lowering a single
crystal growth rate for forming the straight body portion,
temporarily lowering temperature of the melt (heating temperature
by a heater) or the like. By thus temporarily changing the crystal
growth condition, an external diameter of the straight body portion
2 grows larger and the annular shaped convex portion is formed. The
single crystal growth rate and the temperature of the melt (the
heating temperature by the heater) are set in accordance with a
desired size of the convex portion, and a configuration of a CZ
furnace used and components inside the furnace.
[0050] The convex portion 3 can be formed either after forming the
straight body portion 2 or before forming the tail portion 5, or
after forming the shoulder portion 5 and before forming the
straight body portion.
Silicon Crystal Material With Concave Gripped Portion
[0051] FIG. 2 is a sectional view schematically illustrating a
silicon crystal material according to a second embodiment of the
present invention. A silicon crystal material 1 is composed of: a
straight body portion 2; a concave portion (gripped portion) 7 that
is formed in a groove-like shape on a periphery of the straight
body portion 2; a neck portion 4 formed during single crystal
growth of a CZ crystal; a shoulder portion 5 that is continuous
with the neck portion 4 and constitutes an upper portion of the
straight body portion 2; and a tail portion 6 that constitutes a
lower portion of the straight body portion 2. The concave portion
(gripped portion) 7 is formed in a manufacturing process of a
silicon crystal by the CZ method, on a periphery of the straight
body portion, so as to have a diameter smaller than an external
diameter of the straight body portion 2. It should be noted that,
although the concave portion (gripped portion) 7 is formed on the
shoulder portion 5 side in the present embodiment, the present
invention is not limited thereto and the convex portion 3 can also
be formed on the tail portion 6 side.
[0052] Although the diameter of the concave portion (gripped
portion) 7 varies dependent on shape, structure and the like of a
gripper for gripping the silicon crystal material, the diameter of
the concave portion (gripped portion) 7 is preferably smaller than
the external diameter of the straight body portion 2 by about 6 to
20 mm. In addition, a length thereof is preferably about 5 to 10
mm. As used herein, the length means a size corresponding to width
of the concave portion in a vertical direction (a longitudinal
direction of the straight body portion).
Manufacturing Method
[0053] The silicon crystal material 1 with the concave portion 7 as
the gripped portion, similar to the above, can be manufactured in a
conventional manufacturing method of a silicon crystal by the CZ
method. That is, a silicon crystal material is manufactured by:
filling a crucible such as a quartz crucible with a raw material
which is an agglomerate of silicon polycrystal; immersing a seed
crystal into a raw material melt, in which the silicon polycrystal
is melt down by heating by a heater and the like; and growing a
crystal up to a predetermined size, for example 155 mm in diameter
and 1150 mm in length of the straight body portion while rotating
the seed crystal and the crucible in inverse directions. It should
be noted that a crystal growth condition is set in accordance with
a desired diameter of crystal.
[0054] In a crystal growth process, the growth condition is
temporarily changed by, for example, temporarily increasing single
crystal growth rate for forming the straight body portion,
temporarily raising temperature of the melt (heating temperature by
a heater) or the like. By thus changing the crystal growth
condition, growth in external diameter of the straight body portion
2 is suppressed and the concave portion is formed. The single
crystal growth rate and the temperature of the melt (the heating
temperature by the heater) are set in accordance with a desired
size of the concave portion, and a configuration of a CZ furnace
used and components inside the furnace. In addition, the concave
portion 7 can be formed either after forming the straight body
portion 2 or before forming the tail portion 5, or after forming
the shoulder portion 5 and before forming the straight body
portion. Silicon Crystal Material With Constricted Gripped
Portion
[0055] FIG. 3 is a sectional view schematically illustrating
silicon crystal material according to a third embodiment of the
present invention. A silicon crystal material 1 is composed of: a
straight body portion 2; a neck portion 4 formed during single
crystal growth of a CZ crystal; a constricted portion (gripped
portion) 8 positioned between the straight body portion 2 and the
neck portion 4; a shoulder portion 5 that is continuous with the
constricted portion 8 and constitutes an upper portion of the
straight body portion 2; and a tail portion 6 that constitutes a
lower portion of the straight body portion 2. The constricted
portion (gripped portion) 8 is formed in a manufacturing process of
a silicon crystal by the CZ method, to have a rhombus bead shape
(to have a vertical cross section being substantially
diamond-shaped) above the straight body portion 2. It should be
noted that, although the constricted portion (gripped portion) 8 is
formed above the shoulder portion 5 in the present embodiment, the
present invention is not limited thereto and the convex portion 3
can also be formed below the tail portion 6.
[0056] Although the constricted portion (gripped portion) 8 varies
dependent on shape, structure and the like of a gripper for
gripping the silicon crystal material, the constricted portion
(gripped portion) 8 preferably has a rhombus bead shape (has a
vertical cross section being substantially diamond-shaped) of about
20 to 50 mm in maximum diameter and 50 to 200 mm in length.
Manufacturing Method
[0057] The silicon crystal material 1 with the constricted portion
8 as the gripped portion, similar to the above, can be manufactured
in a conventional manufacturing method of a silicon crystal by the
CZ method. That is, a silicon crystal material is manufactured by:
filling a crucible such as a quartz crucible with a raw material
which is an agglomerate of silicon polycrystal; immersing a seed
crystal into a raw material melt, in which the silicon polycrystal
is melt down by heating by a heater and the like; and growing a
crystal up to a predetermined size, for example 155 mm in diameter
and 1150 mm in length of the straight body portion while rotating
the seed crystal and the crucible in inverse directions. It should
be noted that a crystal growth condition is set in accordance with
desired diameter of crystal.
[0058] In a crystal growth process, in formation of a straight body
portion of silicon crystal from a seed crystal, a growth condition
is changed for a portion between the end of necking and beginning
of forming the shoulder portion 5. In other words, in a process of
forming the shoulder portion 5 under a crystal growth condition for
forming the straight body portion 2, at the time where external
diameter thereof reaches a predetermined size, a single crystal
growth rate is raised for narrowing down the external diameter; and
then, at the time where the external diameter is narrowed down to a
predetermined size, the single crystal growth rate is reset to an
original value for crystal growth of the straight body portion,
thus forming the straight body portion 2. In such a configuration,
for example, the constricted portion 8 having a rhombus bead shape
(having a substantially diamond-shaped vertical cross section) of
about 50 mm in diameter and 50 mm in length, is formed above the
straight body portion 2. It should be noted that a condition for
forming the constricted portion 8, in other words change in the
single crystal growth rate and in the temperature of a melt (the
temperature of a heater) can be arbitrarily set in accordance with
a desired size of the constricted portion 8.
[0059] It should be noted that, in a case of forming the
constricted portion 8 below the tail portion 6, the abovementioned
process can be performed under the same growth condition after that
the tail portion 6 is formed. In other words, after forming the
tail portion 6, the single crystal growth rate is lowered for
growing external diameter; and then, at the time where the external
diameter is grown to a predetermined size, the single crystal
growth rate is reset to an original value for forming the
constricted portion of the abovementioned size.
Silicon Crystal Material With Seed Crystal Gripped Portion
[0060] FIG. 4 is a sectional view schematically illustrating a
silicon crystal material according to a fourth embodiment of the
present invention. A silicon crystal material 1 is composed of: a
seed crystal 9; a neck portion 4 formed during single crystal
growth of a CZ crystal; a straight body portion 2; a shoulder
portion 5 that is continuous with the neck portion 4 and
constitutes an upper portion of the straight body portion 2; and a
tail portion 6 that constitutes a lower portion of the straight
body portion 2. The seed crystal 9 is used in the manufacturing
process of the silicon crystal by the CZ method. In other words,
the silicon crystal material 1 is continuously formed with a seed
crystal 9, the neck portion 4 and the straight body portion 2. The
silicon crystal material 1 is obtained as following: the seed
crystal is withdrawn after immersed in the melt; thus a silicon
crystal grows behind the seed crystal; when the silicon crystal
material 1 is removed from a CZ furnace, a portion from the neck
portion 4 to the seed crystal 9 is kept intact. In the silicon
crystal material 1, the seed crystal 9 is used as a gripped
portion.
[0061] In the silicon crystal material 1, since the seed crystal 9
is gripped and maintained suspended, the neck portion 4 is
preferably at least 5 mm in diameter. In a case where the diameter
of the neck portion is less than 5 mm, the neck portion 4 may be
broken in a process of growing an FZ silicon single crystal and
thus the silicon crystal material 1 may drop off. In addition, the
seed crystal 9 more preferably has a bored portion 9a. This allows
the silicon crystal material 1 to be more firmly gripped and
maintained suspended by a gripper (described later).
Manufacturing Method
[0062] The silicon crystal material with a gripped portion of the
seed crystal 9, similar to the above, can be manufactured in a
conventional manufacturing method of a silicon crystal by the CZ
method. That is, a silicon crystal material is manufactured by:
filling a crucible such as a quartz crucible with a raw material
which is an agglomerate of silicon polycrystal; immersing a seed
crystal into a raw material melt, in which the silicon polycrystal
is melt down by heating by a heater and the like; and growing a
crystal up to a predetermined size, for example 155 mm in diameter
and 1150 mm in length of the straight body portion while rotating
the seed crystal and the crucible in inverse directions.
[0063] The silicon crystal materials 1 manufactured as described
above are silicon crystal materials manufactured by the CZ method,
in which a gripped portion, which is gripped by a gripper of an FZ
single crystal manufacturing device, is formed thereon during a
process of manufacturing the crystal. Therefore, unlike a silicon
raw material ingot conventionally used, a mechanical process is not
required for forming the gripped portion, thereby reducing loss of
material in processing and cycle time for manufacturing FZ silicon.
In addition, a large diameter silicon crystal material can be
obtained by the CZ method, and a large diameter FZ silicon single
crystal can be obtained by using this silicon crystal material as a
raw material ingot.
Manufacturing Method of FZ Silicon Single Crystal
[0064] Next, a manufacturing method of an FZ silicon crystal using
the silicon crystal material according to the present invention is
explained hereinafter.
[0065] FIG. 5 is a schematic partial sectional view illustrating an
example of an FZ single crystal manufacturing device according to
the present invention. An FZ single crystal manufacturing device 20
has a similar structure as a conventional FZ single crystal
manufacturing device, and includes: a gripper 22 that grips a raw
material ingot 23 (the silicon crystal material 1) and a superior
axis 21 that is continuous therewith on an upper portion thereof; a
crystal gripper 25 that grips a seed crystal and an inferior axis
24 that is continuous therewith on a lower portion thereof; and an
induction heating coil (a high-frequency coil) 28 therebetween. The
superior axis 21 and the inferior axis 24 allow the raw material
ingot to rotate and to move up and down.
[0066] The abovementioned silicon crystal material 1 manufactured
by the CZ method is, as shown in FIG. 5, gripped by the gripper 22
on the superior axis 21 of the FZ single crystal manufacturing
device 20 that is installed in a chamber (not shown) of an FZ
growth furnace, and set as a silicon raw material ingot 23. A seed
crystal 26 for manufacturing an FZ silicon single crystal is set on
the gripper for lower portion of the crystal 25 on the inferior
axis 24.
[0067] More specifically, the silicon crystal material is set on
the single crystal manufacturing device 20 as follows.
[0068] The silicon crystal material 1 having the convex portion 3
on the straight body portion 2 thereof, as described in the first
embodiment, is gripped by a claw 22c provided on a lower end of a
gripper rod 22b of the gripper 22 that is engaged with the convex
portion 3, as shown in FIG. 6.
[0069] The gripper 22 is not particularly limited as long as a
mechanism is provided for gripping by engaging with the convex
portion 3, the concave portion 7, and the constricted portion 8 of
the gripped portion; and the gripper 22, for example, can be
composed of: a plate-like supportive portion 22a; a plurality
(preferably at least 3 for supporting a weighty silicon crystal
material from a perspective of stability) of gripper rods 22b that
is rotatably attached to the supportive portion 22a; and a crow 22c
that is provided on an end portion of the gripper rod 22b so as to
form a substantially L-shape (see FIG. 6).
[0070] The silicon crystal material 1 having the concave portion 7
on the straight body portion 2 thereof, as described in the second
embodiment, is gripped by the claw 22c provided on a lower end of
the gripper rod 22b of the gripper 22 that is engaged with the
concave portion 7, as shown in FIG. 7.
[0071] In addition, the silicon crystal material 1 having the
constricted portion 8 on the straight body portion 2 thereof, as
described in the third embodiment, is gripped by the claw 22c
provided on a lower end of the gripper rod 22b of the gripper 22
that is engaged with the constricted portion 8, as shown in FIG.
8.
[0072] The silicon crystal material 1 composed of the seed crystal
9, the neck portion 4, and the straight body portion 2, as
described in the fourth embodiment, is gripped at the seed crystal
9 by the gripper rod 22b of the gripper 22 as shown in FIG. 9. In
this case, as a gripper, a pin 22d, which can be taken in and out
toward the seed crystal side, is preferably formed on a side face
of the gripper rod 22b facing the seed crystal 9. In such a
configuration, the pin 22d of the gripper rod 22b is inserted into
the bored portion 9a (see FIG. 4) formed on the seed crystal 9,
thereby maintaining the silicon crystal material 1 suspended more
firmly.
[0073] Subsequently, an apex of the silicon raw material ingot 23
(silicon crystal material 1), which is maintained suspended in the
FX furnace, is preheated by a carbon ring (not shown).
[0074] Thereafter, Ar gas containing nitrogen gas is supplied from
a lower portion of the chamber and discharged from an upper portion
of the chamber, at a furnace pressure of 0.20 MPa, a feed rate of
Ar gas of 50 L/min, and nitrogen concentration inside the chamber
of 0.1%. Next, after heating and melting the apex of the silicon
raw material ingot 23 by the induction heating coil (the
high-frequency coil) 28, the molten apex of the silicon raw
material ingot 23 is fused with the seed crystal 26 and made to be
dislocation-free by necking, the silicon raw material ingot 23 is
brought down and molten while rotating the superior axis 21 and the
inferior axis 24 for supplying a melt to a melt zone 29, and a
lower portion of the melt zone 29 is coagulated and recrystallized,
thereby growing an FZ silicon single crystal 30. In this case, the
superior axis 21 that is a rotational center when the silicon raw
material ingot 23 is growing and the inferior axis 24 that is a
rotational center of the silicon single crystal 30 in
recrystallization are coaxial and rotate around a common rotational
center. In addition, the axes preferably rotate back and forth
alternately and grow the silicon single crystal 30. By rotating
back and forth alternately, a silicon crystal in molten state is
agitated in recrystallization, and thus quality, such as in-plane
resistivity distribution, of the silicon single crystal 30 thus
manufactured can be uniformized. A moving angle of backward and
forward rotation, rotation speed and the like can be arbitrarily
set in accordance with a diameter of the silicon single crystal
30.
[0075] In such a configuration, a dopant that is unavoidably
contained in the silicon raw material ingot (silicon crystal
material) 23 manufactured by the CZ method can be uniformly
distributed in the melt zone and thus the dopant can also be
uniformly distributed in the FZ silicon single crystal 30, thereby
obtaining a silicon single crystal with a superior in-plane
resistivity distribution.
[0076] In addition, the resistivity can be lowered by adding a
dopant of the same conductivity type as that of the dopant
contained in the original silicon raw material ingot 23. On the
other hand, a silicon single crystal 30 of higher resistivity than
the silicon raw material ingot 23 can be obtained by adding a
dopant of an opposite conductivity type.
[0077] Gas doping can be performed according to a well-known
method, by blowing a doping gas on the melt zone 29 at a
predetermined feed rate. For example, in order to make the silicon
single crystal 30 p-type, argon gas containing a minute amount of
diborane (B.sub.2H.sub.6) can be used as doping gas. In order to
make the silicon single crystal 30 n-type, argon gas containing
phosphine (PH.sub.3) can be used as doping gas. Resistivity in a
growth direction of the silicon single crystal 30 can be
uniformized by a method disclosed in Japanese Unexamined Patent
Application Publication No. 2006-267287.
EXAMPLES
[0078] The present invention is described in more detail
hereinafter by means of examples; however, the present invention is
not limited thereto.
Example 1
[0079] A silicon crystal composed of a neck portion, a shoulder
portion, and a straight body portion, for an FZ silicon crystal
material, was prepared by a commonly practiced CZ method, thereby
obtaining a silicon crystal material having a straight body portion
of 155 mm in diameter and 1150 mm in length.
[0080] After forming the straight body portion and before forming a
conical portion that is a tail portion of the crystal, single
crystal growth rate was lowered to about one-third of the single
crystal growth rate for the straight body portion, in order to
temporarily grow crystal diameter, thereby forming a convex portion
in a radial direction. After that, a built-up portion grew to about
10 mm and diameter of the convex portion reached 170 mm, and the
single crystal growth rate was gradually turned back to the
original single crystal growth rate before the change.
[0081] After that diameter of the straight body portion went down
to 155 mm, a conventional tail portion was formed. The crystal
growth was terminated with the tail portion of 50 mm in length,
which was shorter than normal.
[0082] In the abovementioned operation, the convex portion of about
7.5 mm on one side and 20 mm in length could be formed immediately
above the tail portion.
[0083] As a result, a silicon crystal material having a straight
body portion of 155 mm in diameter and 1150 mm in length, with the
convex portion of about 7.5 mm and about 20 mm in length formed
immediately above the tail portion of the crystal, was
manufactured.
[0084] The silicon crystal material thus obtained was loaded into
an FZ furnace by fixing the convex portion with a gripper for
silicon crystal material. Centering was performed for rotating the
silicon crystal material.
[0085] Thereafter, a silicon single crystal was grown by a commonly
practiced FZ method, thereby manufacturing an FZ silicon single
crystal having a straight body portion of 1000 mm in length and 150
mm in diameter.
Example 2
[0086] A neck portion and a shoulder portion were formed by a
normal CZ single crystal growth method, as in Example 1.
Subsequently, immediately after starting formation of a straight
body portion, a single crystal growth rate was temporarily doubled.
By this acceleration, diameter of the crystal went down from 155 mm
to 140 mm at a maximum.
[0087] After that, a length of a concave portion reached about 7
mm, and the single crystal growth rate was gradually turned back to
the original single crystal growth rate before the change, thereby
making the crystal diameter 155 mm, the original value.
[0088] Thereafter, by a conventional operation, the straight body
portion of 155 mm in diameter was grown to 1150 mm in length and
finally a tail portion was formed. The crystal growth was thus
terminated.
[0089] As a result, a silicon crystal material having a straight
body portion of 155 mm in diameter and 1150 mm in length, with the
concave portion of about 15 mm in depth and about 7 mm in length
formed immediately below the shoulder portion of the crystal, was
manufactured.
[0090] The silicon crystal material thus obtained was loaded into
an FZ furnace by fixing the concave portion with a gripper for
silicon crystal material as in Example 1. Centering was performed
for rotating the silicon crystal material.
[0091] Thereafter, a silicon single crystal was grown by a commonly
practiced EZ method, thereby manufacturing an FZ silicon single
crystal having a straight body portion of 1000 mm in length and 150
mm in diameter.
Example 3
[0092] A neck portion was grown to about 50 mm below the seed
crystal by a normal CZ single crystal growth method, as in Example
1, and then a single crystal growth rate was lowered to about
one-fourth and a temperature of a heater was lowered by some
degrees. A diameter of the neck portion, which had been 5 mm, was
thus grown to 30 mm.
[0093] Thereafter, the single crystal growth rate and the
temperature of the heater were gradually turned back to original
values, and then a neck portion of 10 mm in diameter was grown to
about 100 mm.
[0094] Next, a straight body portion was formed by an operation
similar to that of a normal single crystal growth method, and a
silicon crystal material having a straight body portion of 155 mm
in diameter and 1150 mm in length was manufactured.
[0095] As a result, a silicon crystal material having a straight
body portion of 155 mm in diameter and 1150 mm in length, with the
constricted portion of a rhombus bead shape with a maximum diameter
of 30 mm being formed in the neck portion of 150 mm in length, was
manufactured.
[0096] The silicon crystal material thus obtained was loaded into
an FZ furnace by fixing the constricted portion with a gripper for
silicon crystal material as in Example 1. Centering was performed
for rotating the silicon crystal material.
[0097] Thereafter, a silicon single crystal was grown by a commonly
practiced FZ method, thereby manufacturing an FZ silicon single
crystal having a straight body portion of 1000 mm in length and 150
mm in diameter.
Example 4
[0098] A silicon crystal material was manufactured by a normal CZ
single crystal growth method, as in Example 1. In this case, unlike
Examples 1 to 3, the single crystal was grown without temporarily
changing the single crystal growth rate and the temperature of the
heater.
[0099] After crystal growth by the CZ method, the silicon crystal
material thus formed was removed from a CZ furnace in a state where
a seed crystal, a neck portion, and a straight body portion were
successively formed. The silicon crystal material having a straight
body portion of 155 mm in diameter and 1150 mm in length, in which
the seed crystal, the neck portion, and the straight body portion
were linked, was thus manufactured.
[0100] Utilizing the seed crystal of the silicon crystal material
thus obtained, the silicon crystal material was loaded into an FZ
furnace by gripping the seed crystal portion with a gripper that
houses the seed crystal inside and inserts a pin into a bored
portion on the seed crystal. It should be noted that, in loading,
the centering operation for rotation of the silicon crystal
material inside the FZ furnace, which was performed in Examples 1
to 3, was not required since the seed crystal and a main crystal
body (the straight body portion) had a common rotational
center.
[0101] Thereafter, a silicon single crystal was grown by a commonly
practiced FZ method, thereby manufacturing an FZ silicon single
crystal having a straight body portion of 1000 mm in length and 150
mm in diameter.
Comparative Example 1
[0102] A silicon crystal material having a straight body portion of
155 mm in diameter and 1150 mm in length was manufactured according
to a commonly practiced CZ method.
[0103] A shoulder portion or a tail portion of the silicon crystal
material thus obtained was cut off and a groove of 5 mm in depth
and 5 mm in length was formed on a peripheral surface of the
vicinity of the portion being cut off, by a mechanical process.
[0104] Next, the silicon crystal material was loaded into an FZ
furnace by fixing the groove with a gripper for silicon crystal
material. Centering was performed for rotating the silicon crystal
material.
[0105] Thereafter, an FZ silicon single crystal was grown by a
commonly practiced CZ method, thereby manufacturing an FZ silicon
single crystal having a straight body portion of 1000 mm in length
and 150 mm in diameter.
[0106] In comparison with Comparative Example 1, loss of a silicon
crystal material could be reduced by about 7.5 kg (about 11%) per
bar in Examples 1 to 4. In addition, operations such as centering,
for rotation of the silicon crystal material after loading, could
be performed in Examples 1 to 4 with no difference from Comparative
Example 1.
[0107] Furthermore, although it took about 45 minutes for cutting
off and forming the groove in Comparative Example 1, these
operations were not required in Examples 1 to 4 and therefore total
manufacturing time and manufacturing cost could be reduced.
* * * * *